Demagnetizer, solid state

ABSTRACT

A completely solid state demagnetizer including: a circuit including the object to be demagnetized and including a portion for applying DC to the object, and including portions operable for so applying the DC in successively opposite polarities; a first condenser of fixed capacity chargeable substantially instantaneously, and charged constantly by the power source; a second condenser progressively chargeable, of variable capacity, and having limits above and below that of the first condenser; the first condenser, when the second condenser is charged to a value less than itself, energizing the circuit portion operable for applying DC of a first polarity to the object; and the second condenser, when charged to a value greater than that of the first condenser; energizing the circuit portion operable for applying DC of the opposite polarity to the objects; an additional condenser means providing a decaying action for progressively and continuously reducing the value of the voltage applied to the object.

United States Patent Arthur K. Littvvin [72] inventor Lincolnwood, iii.

[2 i Appl. No. 68,625

[22] Filed Sept. 1, 197i) [45] Patented Dec. 7, 1971 [73] AssigneeLittwin Family Trust No. 1

Chicago, Ill.

s4 DEMAGNETIZER,SOLID STATE UNITED STATES PATENTS 3,086,i48 4/1963Soneki 317/i57.5

Primary Examiner-L. T. Hix Attorney-Paul H. Gallagher ABSTRACT: Acompletely solid state demagnetizer including: a circuit including theobject to be demagnetized and including a portion for applying DC to theobject, and including portions operable for so applying the DC insuccessively opposite polarities; a first condenser of fixed capacitychargeable substantially instantaneously, and charged constantly by thepower source; a second condenser progressively chargeable. of variablecapacity, and having limits above and below that'of the first condenser;the first condenser, when the second condenser is charged to a valueless than itself, energizing the circuit portion operable for applyingDC of a first polarity to the object; and the second condenser, whencharged to a value greater than that of the first condenser; energizingthe circuit portion operable for applying DC of the opposite polarity tothe objects; an additional condenser means providing a decaying actionfor progressively and continuously reducing the value of the voltageapplied to the object.

DEMAGNETIZER, SOLID STATE OBJECTS OF THE INVENTION The present inventionrelates to demagnetizing of an-object of the general character in whichDC is applied to the object in successive steps of opposite polarity andin which the voltage in the successive steps is gradually reduced,whereby at the final step the voltage is at or near 0, and the object isaccordingly substantially demagnetized.

Dernagnetizing as just referred-to is generally known, as representedfor example in my prior US. Pat. No. 2,825,854, dated Mar. 4, I958.

A broad object of the present invention is to provide a demagnetizingcircuit and method of demagnetizing of the foregoing general nature,which is of completely solid state nature.

Another broad object is toprovide a solid state demagnetiz ing circuitof the character referred to having a novel arrangement of condensers inmutually opposed relation oneof which is of fixed capacity and the otherof variable capacity, each of the condensers, when of a greater chargedcondition than the other, controlling the polarity of the DC applied tothe object, and the two together operable for applying the DC'inmutually opposed steps throughout a series for accomplishing thedemagnetizing operation.

Another object is to provide a solid state circuit for demagnetizing ofthe character just immediately referred to which includes means formaintaining the voltage on the condenser means at a point close to thatnecessary for activating each condenser over the other, so that uponbuildup of voltage for the particular condenser, only a minimum of suchbuildup is required for triggering that condenser and so that itovercomes the opposed condenser.

A still further object is to provide a circuit for demagnetizing of theforegoing character including novel means for reducing the DC applied tothe object, so that when the DC is reversed under control of thereversing means referred to, i.e., the condensers reduce the magnetismof the object in the successive steps.

A still further object is to provide apparatus of the kind justimmediately referred to and including means for shutting off thedemagnetizing circuit when the voltage of the DC as applied to theobject is substantially at 0, wherein that shutting off means isindependent of the reversing means, whereby to effectively shut ofi' theapparatus when the magnetism of the object to be demagnetized issubstantially accomplished.

DESCRIPTION OF A-PREFERRED EMBODIMENT In the drawings:

The single figure is a diagram of a completely solid state arrangementfor demagnetizing an object. I

Referring in detail to the circuit, .a magnetic chuck is shown (bottomcenter), of a kind commonly used in a machine tool, such for example asin a grinder and utilized in the reciprocating table for holding theworkpiece to be ground. Such a chuck is represented in FIG. 5 of myprior patent referred to above (see No. 16, and the workpiece No. 17 inthat patent). The magnetic chuck itself does not form a part of theinvention, and is well-known, as is the overall and general arrangementand method for demagnetizing the chuck and the workpiece thereon. lnthecircuit the portion at the bottom enclosed in dot-dash lines andindicated at 12 represents the reversing means utilized in thedemagnetizing operation, and the other portion of the circuit thecontrol means for controlling that reversing means.

The circuit represented in the drawing includes a suitable AC source 14from which conductors 16, 18 lead, and in which are included switchmeans 20, 22 which may be ganged. Condensers 24, 26 include principalcontrol elements for reversing the polarity of the DC applied to thechuck. The condenser 24 is connected between the main lines 18, 16through conductors 27, 28, 29, 30 and 31, the conductors 27 and 31having rectifiers 32, 33 therein. The condenser 26 is connected betweenthe lines 18, 16 through conductor 34 having a rectifier 35 therein, andleading to the cathode of an SCR (silicon controlled rectifier) 36.Leading from the plate are conductors 37, 38, 39, the latter containingthe condenser 26 and leading through conductors 30, 31 to the line 16.Connected across the conductors 37, 30 is a conductor 40 containingseries adjustable resistors 42, 44 which are connected across thecondenser 26. 7

Another conductor 46 leads from the conductor 34 to another conductor 48connected with the gate of the SCR 36 holding the SCR in conductingcondition. The conductor 46 also connects with another conductor 50leading to the plate of an SCR 52, and leading from the plate of thelatter is another conductor 54 connected with an additional conductor 56connected between the resistors 42, 44. Another adjustable resistor 58is interconnected between the conductors 54, 30. The gate of the SCR 52is connected with another conductor 60 which is connected'with theconductor 56. A zener diode 62 is connected across the condenser 24.

.Associated with the condensers 2,4, 26 are transistors 64, 66respectively (upper), and associated with those transistors are SCRs 68,70 respectively (top), and controlled in a manner referred to below. Therectifiers, transistors and SCRs may be referred to each and genericallyas valve means or gate means.

Connected between the main lines l6, l8 is a conductor 72 having seriesprimaries 74F, 76F of transformers 74, 76, and the line has back-to-backrectifiers 78, 80 therebetween. Also connected between the main linesisanother conductor 82 having series primaries 84F, 86F of transformers84, 86, and including back-to-back rectifiers' 88, 90 therebetween. Thesecondaries of these transformers re found at the bottom of the circuit,having the same reference numerals with the subscript S.

The secondaries just referred to are incorporated in the portion 12 atthe bottom of the circuit, and are individually connected with the gatesof SCRs as follows: 748 with SCR 92, 76S with SCR 94, 84S with SCR 96,and 865 with SCR 98. These SCRs are respectively arranged inback-to-back relation, i.e. the SCRs 92, 94 providing unidirectionalcurrent in one direction to the chuck10, and the SCRs 9 6, 98 providingunidirectional current in the other direction. The chuck is connectedwith-a conductor 104 center-tap connected with a primary 106? of atransformer 106, the primary being-connected across the main lines 16,18, and connected respectively the SCR systems, viz, 92, 98 at one endand 94, 96 at the other end, completing circuit through the chuck. Thistransformer 106 includes secondaries 106S1 (top), 10652 (lower right),and 10653 (lower center).

Upon energization of the primary 106P (bottom) the chuck 10 isenergized, and according to which of the secondaries directly connectedwith that primary are energized, the chuck is magnetized at one or theother direction: when the secondaries 74S, 768 are energized, the chuckis magnetized in a first direction, or first polarity, and when thesecondaries 848, 868 are energized, the chuck becomes energized ormagnetized in the opposite or second direction, or second polarity. The

back-to-back arrangement as to the secondaries 74S, 76S, and

the other secondaries 84S, 86S, together with the arrangement of theprimary 106P in itself is known and the means for controlling theenergization of those coils by the remaining portion of the circuit isof the essence of the invention.

Included in the circuit is switch means 108 (right, upper and lower),including two individual switches 108a and 108b, preferably. gangedtogether and movable between ON 'and DEMAG (demagnetizing) positions.

Leading from the first switch 108a is a conductor connected with theconductor 38 and leading to a variable resistor 112 and connected withanother conductor 114 which includes an adjustable resistor 1 16, andalso connected with a conductor 115. A return conductor 117 leads fromthe conductor 114 to the ON terminal of the switch 108a. Leading fromthe adjusting element of the resistor 1 16 is a conductor 118 connectedwith the base of the transistor 64 and leading from the emitter of thattransistor is another conductor 120 connected with a conductor 122 whichleads to the emitter of the transistor 66. Leading from the base of thetransistor 66 are conductors 124, 125 connected with the conductor 110.interconnecting the conductors 118, 124 are additional conductors 126,128, respectively, including resistors 130, 132, and connected withthese conductors between the resistors is another conductor 134 whichincludes the secondary 10681 and is connected with another conductor 136leading in one direction to a conductor 137 which includes a primary138P and in the other direction to a conductor 139 including a primary140P. The conductor 137 leads to the anode of the SCR 68 while the otherconductor 139 leads to the anode of the SCR 70.

The transformer 138 includes a secondary 138S (center, left) while thetransformer 140 includes a secondary 140S (center, right). The secondary138$ leads to the base of a transistor 142 while the other secondary140S leads to the base of a transistor 144. Leading from the emitter ofthe transistor 142 is a conductor 143 connected with the conductor 72between the rectifiers 78, 80, and similarly a conductor 145 leads fromthe emitter of the transistor 144 and is connected with the conductor 82between the rectifiers 88, 90. Leading from the collectors of thetransistors 142, 144, is a conductor 146 connected with which is anotherconductor 148 center-tapped to the secondary 106S3.

Connected across the main lines 16, 18 are additional conductors 150,152 leading respectively to the anodes of SCRs 154, 156, and thecathodes thereof are interconnected by conductors 179, 181 which alsoconnect with the conductor 148. The gates of the SCRs 154, 156 areconnected at opposite ends to the secondary 106S3.

Leading center-tapped from the secondary 10683 is a conductor 160connected with the emitter of a transistor 162 and connected with thebase of that transistor is another conductor 164 leading to thecollector of another transistor 66. The emitter of the transistor 166 isconnected through a conductor 168 to the collector of the transistor 166and to another conductor 170 leading to the ON terminal of the switch108b. A conductor 172 leads from the base of the transistor 166 to thecommon terminal of the switch 108b. Leading from the DEMAG terminal ofthe switch 108!) is a conductor 174 connected with the secondary 106S2.

1n the use of a magnetic chuck it is utilized for holding a workpiece onwhich a work operation is performed, such as grinding, and for thatpurpose it must be fully magnetized. Although the principal purpose ofthe present invention is to demagnetize that chuck, and the workpiecethereon, it is necessary that the circuit also directly control allphases of control of the chuck, in order to perform the demagnetizingoperation. Specifically, it may be desired to turn off the chuck toremove a piece for testing purposes and often that piece is again placedon the chuck and a further grinding operation is performed thereon. Thusthe circuit is utilized for turning on and off the chuck as well as fordemagnetizing it. The present circuit is interposed in the controlcircuit normally provided for energizing the chuck and operates to turnon and off that circuit. To put the circuit of the present inventioninto operation, in an initiating step, the switch means 20, 22, is ofcourse closed which energizes all of the elements then directlyconnected with the main lines 16, 18, including the primary 106P. Thendepending on whether the grinding operation is to be performed, or ademagnetizing operation, the switch means 108 is thrown to correspondingposition, and normally it is first thrown to ON position for energizingthe chuck.

For convenience in describing the operation, reference is made first tothe DEMAG, or demagnetizing position and to establish that position,after the main switch means 20, 22 is closed, the switch means 108 isthrown to its full line position. A circuit is established from the mainline 18 through the conductor 27, rectifier 32, conductors 28, 29, 30,31 to the line 16. This charges the condenser 24 instantaneously. At thesame time, a circuit is established through conductor 34, SCR

36, this SCR being turned on through the conductor 46; the circuitcontinues through conductors 37, 38, 39, the condenser 26, andconductors 30, 31. The condenser 26 charges slowly from its lower valueof e.g., l0 volts to its upper value of, e.g., 40 volts, while thecapacity of the condenser 24 may be of 25 volts. 7

The condensers 24, 26 are opposed, the negative sides thereof beingconnected with the conductor 30 and with an additional conductor whichconnects with the conductor 114. Upon the condenser 24 reaching itscapacity charge, it controls the transistors 64, 66 as follows: from thepositive side, through conductors 29, 28, adjustable resistor 116,conductor 118 applying a positive charge on the transistor 64 andturning it on; it continues through conductors 120, 123, 145, 149, thecollector of the transistor 66 and from the base thereof, throughconductors I24, 125, 110, 39 to the condenser 26 and the negative ofcondenser 24. The transistor 64 is thus turned on and the transistor 66is turned off. A similar circuit is established through the condenser 26and the transistor 66 when the condenser 26 becomes charged and takesover, as referred to below. When the transistor 64 is turned on, itturns on the SCR 70, and similarly, when the transistor 66 is turned on,it turns on' the SCR 68. I 5

Upon turning on the the SCRs 70, 68, the respective primaries P, 138Pare energized, and in a first case, the energized primary 1401 energizesthe secondary 140$ (center, right) and the latter completes a circuitthrough the transistor 144 and turns on the latter. The secondary 106S3(center lower) is energized, which turns on the SCRs 154, 156 inrespective half cycles, and upon turning on of the transistor 144, theprimaries 84?, 86? are energized in respective half cycles, and they inturn energize the secondaries 84S, 86S (bottom) and establish acontinuous circuit in those half cycles of a first polarity through thechuck l0 and the primary 106P for energizing the chuck. Thisenergization occurs and persists throughout the range of effectivenessof the condenser 24, until the condenser 26 takes over. 7

Although the charge on the condenser 24 controls the transistor 64 asreferred to, it remains constantly and fully charged by the main lines,and while the condenser 24 so controls the transistor 64, the charge onthe condenser 26 builds up and when it reaches its maximum charge, e.g.,40 volts, it predominates and reverses the circuit arrangement, turningon the transistor 66 and the SCR 68, and turning off the transistor 64and the SCR 70, in a circuit similar to the circuit including thecondenser 24 as referred to above. Energization of the primary 1381pursuant to turning on of the transistor 66 and SCR 68, energizes thesecondary 138S (center, left) which turns on the transistor 142 andcompletes a circuit for energizing the primaries 74F, 761 in respectivehalf cycles. The latter primaries in turn energize the secondaries 74S,76S (bottom) and complete a circuit through the chuck 10 and primary1061 in corresponding half cycles, and in conjunction with thesecondaries 848, 865, as described above, maintain a DC circuit throughthe chuck. The voltage thus established is of the second polarity oropposite that of the first step.

Upon decay of the voltage of the condenser 26, as determined by theresistors 42, 44, 50 its minimum value which in the assumed example is10 volts, it shuts off and the condenser 24 having remained charged,again predominates and establishes a controlling circuit through thetransistor 64 and SCR 70. This continues until the voltage in thecondenser 26 again builds up to its maximum capacity.

The effectiveness of the condenser 24, 26 on the reversals of polarityon the chuck are controlled by the transistors 162, 166 which in turnare controlled by the switch 108 b. The secondary 106S2 normally remainsenergized, placing a charge on the condenser 186, and when the switch108!) is thrown to DEMAG position, it removes the voltage supply fromthe condenser 186 and the latter discharges, the negative bias controlsthe transistor 162 and therethrough, the transistor 166, and when thischarge is expended, the transistor 166 shuts off. During the one and offperiods of the condenser 186 and control thereby, the oneor the other ofthe secondaries 140$, 1388 is energized, and through the primaries 84P,86P, or 74P, 76P, control the polarity'the DC imposed on the chuck asdescribed producing gradually decreasing periods of opposite polarityand the desired demagnetizing for predetermining the charge on thecondenser 186, and the resulting decaying action is independent of thecharge on cles and the condensers retain their charges throughout aplueither of the condensers 24, 26; when the action of the condenser 186is terminated, the voltage of the chuck 10 is at 0,

or substantially zero, and any .further reversing action by thecondensers 24, 26 thereon,is of no effect.

Another feature of the invention is a means for accuratelycontrollingthe points of effectiveness of the transistors 64, 66. Theresistors 130, 132 are connectedrespectively with the bases of thetransistors and constantly provide a voltage thereon which is slightlyless than the voltage required for turning them on. Thenupon theimposition of the voltage as provided by the condensers 24, 26 on therespective transistors, the latter need be only a very small incrementwhereby only a very small additional voltage is required under thecontrol of the condensers 24, 26 to trigger the transistors. Accordinglythe transistors are rendered more accurately responsive than wouldotherwise be provided for.

lclaim: g

1. Solid state demagnetizing means comprising a circuit adapted tobeconnected with an electrical source and with an Object'to bedemagnetized,'the circuit including means for applying DC to the objectand for applying it in successive steps of opposite polarity,

a first condenser 'of fixed maximum capacity constantly chargeable andsubstantially instantaneously charged by the source,

a second condenser relatively slowly and progressively chargeable by thesource, and adjustable through a range of maximum capacity extendingabove and below that of the first condenser,

and means responsive to and controlled by the first condenser operative,when the second condenser is charged to 'a value less than thatof thefirst condenser, for effecting application of DC of a first polarity tothe object,

means responsive to and controlled by the second condenser operative,when it is charged to a value greater than that of the first condenser,for effecting application of DC of the opposite polarity to the object,

and means for reducing the value of the voltage appliedto the objectduring the reversals of polarity as controlled by the first and secondcondensers.

2. Demagnetizing means according to claim 1 and including a first and asecond transistors related to the condensers, the condensersrespectively controlling the transistors by rendering the correspondingtransistor conducting and the other nonconducting, and, each condenserbeing operative for so controlling the respective transistorupon itspredominance over the other, and the transistors operative forcontrolling the application of DC of respective opposite polarities tothe object.

3. Demagnetizing means according to claim 2 and including first andsecond SCR's related to and controlled by the first and secondtransistors, and transformer means controlled by the SCR's andthemselves controlling the application of DC to the object.

4. A demagnetizing means according to claim 1 adapted for connectionwith an AC source and wherein each condenser is operative throughout arange including a plurality of AC cyrality of AC cycles,and the chargesdecay independently of the AC cycles.

5. Solid state demagnetizingmeans comprising a circuit adapted to beconnected with an AC source and with an object to be demagnetized,

a first charging transformer and rectifier means for effecting a DC of afirst polarity and imposing it on the object, a second chargingtransformer and rectifier means for effecting DC of a second polarityand imposing on the obsource, rectifier means interposed between thesource and the first condenser,

a second condenser relatively slowly and progressively chargeable by thesource, and adjustable through a range of maximum capacity extendingabove and below that of the first condensen rectifiers means interposedbetween the source and the second condenser,

means responsive to and controlled by the first condenser operative,when the second condenser is charged to a value less than that of thefirst condenser, for energizing the first charging transformer andthereby magnetizing the object in the corresponding first polarity,means responsive to and controlled by the second condenser operative,when it is charged to a value greater than that of the first condenser,for energizing the second charging transformer and thereby magnetizingthe object in the corresponding opposite polarity, valve meansoperatively interposed between the condensers and the chargingtransformers, I the first condenser during a predetermined value ofcharge thereon greater than that of the second condenser, being operablefor holding the corresponding valve means in the respective conductivecondition and the corresponding charging transformer in energizedcondition for imposing DC of a first polarity of the object,

. the second condenser during a predetermined value of chargcthereongreater than that of the first condenser, being operable for. holdingthe corresponding valve means in the respective conductive condition andthe corresponding charging transformer in energized condition forimposing DC of the opposite polarity on the object,

and means for reducing the value of the voltage imposed on the objectthroughout a predetermined range independentlyof the periods ofenergization of the condenser means and corresponding energization ofthe charging transformers.

6. Demagnetizing means according to claim 5 wherein the means forreducing the voltage includes additional condenser means chargeable fromthe AC source, and means for controlling the discharging effect of theadditional condenser means and corresponding range of the control of thefirst mentioned condenser means throughout a predetermined range.

7. Demagnetizing means according to claim 6 wherein the means forcontrolling the discharge of the additional condenser means establishesa range of effectiveness thereof greater than the range of discharge ofeither of the first and second condensers and independently thereof.

8. Demagnetizing means according to claim 6 wherein the first and secondcondensers are constantly chargeable by the source, and the circuitincludes means normally holding the charging transformers in deenergizedcondition, and manually controlled means for actuating the means forcontrolling the discharge of the additional condenser means and therebyenergizing the charging transformers.

9. Demagnetizing means according to claim 8 wherein the period ofdischarge of the additional condenser means is greater than that ofeither the first or second condensers.

10. Demagnetizing means according to claim 9 and including transformermeans for energizing the additional condenser means, this lasttransformer means being utilized also for controlling the chargingtransformers.

11. Solid state demagnetizing means including a circuit adapted forconnection to an AC source and to an object to be demagnetized,comprising I a first condenser of fixed maximum capacity connected withthe source, constantly chargeable and substantially instantaneouslycharged by the source, with rectifier means interposed between thesource and the first condenser,

a second condenser relatively slowly and progressively chargeable,connected with the source and adjustable through a range of maximumcapacity extending above and below that of the first condenser, withrectifier means interposed between the source and the second condenser,

a transistor associated with each condenser and controlled thereby,

an SCR related to each transistor and controlled thereby,

each condenser being operative to energizing its related transistorwhile deenergizing the opposite transistor and the transistors beingcorrespondingly operative for energizing the corresponding SCRs whenthey themselves are energized,

transformer means for controlling the object including a maintransformer energized directly by the source, and back-to-backtransformers related to each of opposite polarities of DC and includingassociated back-to-back SCRs directly related to the back-to-backtransformers,

a first pair of transformers having primaries in series connected withthe source and having back-to-back rectifiers therebetween and includingsecondaries forming parts of the back-to-back transformers associatedwith the object,

a second pair of transformers having primaries in series connected withthe source and having back-to-back rectifiers therebetween and includingsecondaries forming posts of the back-to-back transformers associatedwith the object, in the opposite polarity of the DC conductorsrespectively center-tapping the first pair of transformer primaries andthe second set of transformer primaries, I

SCRs connected with the center tappings,

additional transformers having primaries controlled by the firstmentioned SCRs and secondaries controlled by the last mentioned SCRs,

and means for controlling the application of DC to the object to bedemagnetized including transformer means controlled by the lastmentioned SCRs and including the second and third SCRs in a subcircuit,the transformers above mentioned being constantly energized under thecontrol of the first and second condensers, throughout a rangeindeterminate in length,

control means for terminating the application of DC to the object to bedemagnetized including an additional condenser operative when chargedfor energizing the last mentioned transformer and thereby energizing thetransformer controlling the object to be demagnetized,

said additional condenser being constantly charged, and the circuitincluding means normally disconnecting the additional condenser from thelast mentioned transformer,

and manually control means for connecting the additional condenser withthe last mentioned transformer whereby that transformer is energizedthroughout the period of decay of the additional condenser and duringthat period the last mentioned transformer energizes the transformerdirectly controlling the object to be demagnetized and after the decayof the additional condenser it becomes deenergized and the circuit isopened to the object to be demagnetized,

the period of decay of the additional condenser being greater than atleast the period of energization of each of the first and secondcondensers.

1. Solid state demagnetizing means comprising a circuit adapted to beconnected with an electrical source and with an object to bedemagnetized, the circuit including means for applying DC to the objectand for applying it in successive steps of opposite polarity, a firstcondenser of fixed maximum capacity constantly chargeable andsubstantially instantaneously charged by the source, a second condenserrelatively slowly and progressively chargeable by the source, andadjustable through a range of maximum capacity extending above and belowthat of the first condenser, and means responsive to and controlled bythe first condenser operative, when the second condenser is charged to avalue less than that of the first condenser, for effecting applicationof DC of a first polarity to the object, means responsive to andcontrolled by the second condenser operative, when it is charged to avalue greater than that of the first condenser, for effectingapplication of DC of the opposite polarity to the object, and means forreducing the value of the voltage applied to the object during thereversals of polarity as controlled by the first and second condensers.2. Demagnetizing means according to claim 1 and including a first and asecond transistors related to the condensers, the condensersrespectively controlling the transistors by rendering the correspondingtransistor conducting and the other nonconducting, and each condenserbeing operative for so controlling the respective transistor upon itspredominance over the other, and the transistors operative forcontrolling the application of DC of respective opposite polarities tothe object.
 3. Demagnetizing means according to claim 2 and includingfirst and second SCR''s related to and controlled by the first andsecond transistors, and transformer means controlled by the SCR''s andthemselves controlling the application of DC to the object.
 4. Ademagnetizing means according to claim 1 adapted for connection with anAC source and wherein each condenser is operative throughout a rangeincluding a plurality of AC cycles and the condensers retain theircharges throughout a plurality of AC cycles, and the charges decayindependently of the AC cycles.
 5. Solid state demagnetizing meanscomprising a circuit adapted to be connected with an AC source and withan object to be demagnetized, a first charging transformer and rectifiermeans for effecting DC of a first polarity and imposing it on theobject, a second charging transformer and rectifier means for effectingDC of a second polarity and imposing on the object, a first condenser offixed maximum capacity constantly chargeable and substantiallyinstantaneously charged by source, rectifier means interposed betweenthe source and the first condenser, a second condenser relatively slowlyand progressively chargeable by the source, and adjustable through arange of maximum capacity extending above and below that of the firstcondenser, rectifiers means interposed between the source and the secondcondenser, means responsive to and controlled by the first condenseroperative, when the second condenser is charged to a value less thanthat of the first condenser, for energizing the first chargingtransformer and thereby magnetizing the object in the correspondingfirst polarity, means responsive to and controlled by the secondcondenser operative, when it is charged to a value greater than that ofthe first condenser, for energizing the second charging transformer andthereby magnetizing the object in the corresponding opposite polarity,valve means operatively interposed between the condensers and tHecharging transformers, the first condenser during a predetermined valueof charge thereon greater than that of the second condenser, beingoperable for holding the corresponding valve means in the respectiveconductive condition and the corresponding charging transformer inenergized condition for imposing DC of a first polarity of the object,the second condenser during a predetermined value of charge thereongreater than that of the first condenser, being operable for holding thecorresponding valve means in the respective conductive condition and thecorresponding charging transformer in energized condition for imposingDC of the opposite polarity on the object, and means for reducing thevalue of the voltage imposed on the object throughout a predeterminedrange independently of the periods of energization of the condensermeans and corresponding energization of the charging transformers. 6.Demagnetizing means according to claim 5 wherein the means for reducingthe voltage includes additional condenser means chargeable from the ACsource, and means for controlling the discharging effect of theadditional condenser means and corresponding range of the control of thefirst mentioned condenser means throughout a predetermined range. 7.Demagnetizing means according to claim 6 wherein the means forcontrolling the discharge of the additional condenser means establishesa range of effectiveness thereof greater than the range of discharge ofeither of the first and second condensers and independently thereof. 8.Demagnetizing means according to claim 6 wherein the first and secondcondensers are constantly chargeable by the source, and the circuitincludes means normally holding the charging transformers in deenergizedcondition, and manually controlled means for actuating the means forcontrolling the discharge of the additional condenser means and therebyenergizing the charging transformers.
 9. Demagnetizing means accordingto claim 8 wherein the period of discharge of the additional condensermeans is greater than that of either the first or second condensers. 10.Demagnetizing means according to claim 9 and including transformer meansfor energizing the additional condenser means, this last transformermeans being utilized also for controlling the charging transformers. 11.Solid state demagnetizing means including a circuit adapted forconnection to an AC source and to an object to be demagnetized,comprising a first condenser of fixed maximum capacity connected withthe source, constantly chargeable and substantially instantaneouslycharged by the source, with rectifier means interposed between thesource and the first condenser, a second condenser relatively slowly andprogressively chargeable, connected with the source and adjustablethrough a range of maximum capacity extending above and below that ofthe first condenser, with rectifier means interposed between the sourceand the second condenser, a transistor associated with each condenserand controlled thereby, an SCR related to each transistor and controlledthereby, each condenser being operative to energizing its relatedtransistor while deenergizing the opposite transistor and thetransistors being correspondingly operative for energizing thecorresponding SCR''s when they themselves are energized, transformermeans for controlling the object including a main transformer energizeddirectly by the source, and back-to-back transformers related to each ofopposite polarities of DC and including associated back-to-back SCR''sdirectly related to the back-to-back transformers, a first pair oftransformers having primaries in series connected with the source andhaving back-to-back rectifiers therebetween and including secondariesforming parts of the back-to-back transformers associated with theobject, a second pair of transformers having primaries in seriesconnected with the source and having back-to-back rectifiersthErebetween and including secondaries forming posts of the back-to-backtransformers associated with the object, in the opposite polarity of theDC, conductors respectively center-tapping the first pair of transformerprimaries and the second set of transformer primaries, SCR''s connectedwith the center tappings, additional transformers having primariescontrolled by the first mentioned SCR''s and secondaries controlled bythe last mentioned SCR''s, and means for controlling the application ofDC to the object to be demagnetized including transformer meanscontrolled by the last mentioned SCR''s and including the second andthird SCR''s in a subcircuit, the transformers above mentioned beingconstantly energized under the control of the first and secondcondensers, throughout a range indeterminate in length, control meansfor terminating the application of DC to the object to be demagnetizedincluding an additional condenser operative when charged for energizingthe last mentioned transformer and thereby energizing the transformercontrolling the object to be demagnetized, said additional condenserbeing constantly charged, and the circuit including means normallydisconnecting the additional condenser from the last mentionedtransformer, and manually control means for connecting the additionalcondenser with the last mentioned transformer whereby that transformeris energized throughout the period of decay of the additional condenserand during that period the last mentioned transformer energizes thetransformer directly controlling the object to be demagnetized and afterthe decay of the additional condenser it becomes deenergized and thecircuit is opened to the object to be demagnetized, the period of decayof the additional condenser being greater than at least the period ofenergization of each of the first and second condensers.